The invention relates to a bone plate system comprising a bone plate, a pressure plate and a bone screw. The bone plate comprises a through-hole having a seat surface with a variable angle for the bone screw. In a connected state of the system, the bone screw is inserted into the through-hole and the head of the bone screw is enclosed between the bone plate and the pressure plate. A screw connection comprising two fastening screws is provided for fastening the pressure plate to the bone plate.
Bone plates of this kind are fixed to the bone by guiding the bone screw through the through-hole and screwing it into the bone substance. The bone plates are used, for example, to fix bones or bone fragments relative to each other. Other uses are also possible, for example ones in which the bone plate is an element of a prosthesis, such as a joint prosthesis.
Since the seat surface of the through-hole is designed such that it can receive the bone screw at different angles, the surgeon is able, during the operation, to freely choose, within certain limits, the angle at which he screws in the bone screw. He is thus able to insert the bone screw in the way that best corresponds to the anatomical conditions.
The pressure plate is then connected to the bone plate such that the head of the bone screw is clamped between the pressure plate and the bone plate. The bone screw is thus fixed at the selected angle relative to the bone plate. The angle stability between the bone screw and the bone plate has the effect that less load is transmitted between the bone screw and the bone substance per unit of surface area, as a result of which the bone substance is preserved. A bone plate system of this kind is known from EP 0 201 024 A1, for example.